The present invention pertains generally to testing systems. More particularly, the present invention pertains to systems for testing audio cables. The present invention is particularly, but not exclusively, useful as a hand-held audio cable tester which uses the phantom power present in an audio cable to test the cable without requiring access to both ends of the cable.
Recording studios, broadcast studios and public address systems all utilize audio cables to interconnect microphones and professional audio equipment. Different users of the studio/public address systems, however, have different operational requirements, which often requires a reconfiguration of the connections, or cabling, between the microphones and the audio equipment. These constant configuration changes, as well as damage from performance and normal wear-and-tear, can cause degradation in the performance of the cables. Thus, before each use, the cables should be checked to determine if the cables are working properly, or if repair and/or replacement of the cable is required. New cables should be also checked prior to any use within a cabling configuration.
Heretofore, it has been possible to test standard audio cables with standard general purpose electrical test equipment such as ohmmeters. Testing with such equipment, however, tends to be slow, laborious, and frequently erroneous. It requires multiple individual tests to confirm that all possible cable fault conditions are not present. This makes verifying a cable""s suitability for usage very slow and laborious.
In order to expedite the cable testing process, several audio cable testers have been created. These testers can indicate all possible cable fault conditions at once simply by plugging both ends of an audio cable into the tester. This allows for quick and reliable testing, provided both ends of the cable are near each other and are readily accessible. Unfortunately, this is usually not the case in typical implementations of audio cabling. Often, audio cables are several hundred feet in length and are permanently or semi-permanently installed from room to room or from a stage to a control position through a conduit. Accessing both ends of the cable in order to plug them into a typical cable tester is difficult at best and often impossible.
U.S. Pat. No. 4,227,146, which issued to Hodge for a device called xe2x80x9cCable Tester For Locating Shorts Discontinuities And Reversals In Multi-Conductor Cablesxe2x80x9d, discloses a cable tester having a constant current power supply and circuitry for connecting the ends of the cable across the power supply. Hodge further discloses a Y-shaped cable which can be attached to the tester for checking the cable when only one end thereof is accessible. The device as disclosed by Hodge, however actually increases the amount of cable to be tested, as the Y-shaped cable must also be checked for continuity.
U.S. Pat. No. 5,285,163, which issued to Liotta for an invention entitled xe2x80x9cElectrical Cable Continuity And Voltage Testerxe2x80x9d, discloses a hand-held device for testing studio cables. For the device as disclosed by Liotta, a tester has one end formed as a plug for engaging an extension cable, and a switch activation means for illumination a plurality of indicators according to the condition of the tested cable. Liotta, however, also requires a battery for activating the device. The battery configuration increases the internal circuitry required for the device, and further makes the tester inconvenient, and even unreliable, as battery failure renders the device inoperative.
Heretofore, cable testers have not made use of a feature, phantom power, which is standard in mixing consoles and microphone preamplifiers that are used in cabling configurations. Specifically, most cabling configurations include a mixing console which supplies a current limited direct current (DC) voltage that is required for the operation of certain types of microphones. Typically, one end of the cable is plugged into the mixing console, while the other end is connected to the microphone. During operation, the mixing console applies the DC voltage through the cable to the microphone. Cables which are energized in this manner are said to have phantom power.
Most cables have three connections, or pins. When a cable is energized with phantom power, one pin (Pin 1) becomes grounded, and a DC voltage potential is established from the other two pins (Pins 2 and 3) to grounded Pin 1. Further, pins 2 and 3 are electrically isolated from each other. What is desired is a cable testing system that makes use of the DC voltage potential supplied by the phantom power to verify the operating condition of the cables. Such a tester would have a simplified construction, as the tester would not need its own power source. Further, a cable testing system that uses phantom power would allow for testing of a single end of a cable, without requiring access to the other end to complete an electrical circuit.
In light of the above, it is an object of the present invention to provide a cable testing system that tests audio cables when only one cable end is accessible by utilizing the phantom power found on typical audio mixing equipment. It is another object of the present invention to provide a cable testing system that quickly indicates the operating condition of a cable, and, if the cable is inoperative, describes specifically what is wrong with the cable. It is a further object of this invention to provide a cable testing system with a separate direct current (DC) power source to allow testing of audio cables which do not have phantom power. Yet another object of the present invention is to provide a cable testing system that tests audio cables when the ends of the cable are not in close proximity to each other. Another object of the present invention is to provide a cable testing system that is relatively easy to manufacture in a cost effective manner.
The cable tester of the present invention includes a receive unit which comprises a cylindrical housing with open ends, a receive plug that is inserted into one end of the housing and fixed thereto, and an indicating means that is mounted within the other end of the housing. The indicating means comprises a plurality of light-emitting diodes (LED""s), which are electrically connected to the plug via circuitry that is internal to the housing. When the receive plug is inserted into the receptacle end of a cable with phantom power, the phantom power energizes the receive plug and the LED""s, which illuminate according to the operating condition of the cable. This allows the cable to be tested when only one end of the cable is accessible.
The device of the present invention further includes a send unit which comprises a cylindrical casing having open ends, a send receptacle and a send DC voltage source. The send receptacle is inserted into one end of the casing and fixed thereto, while the send voltage source, preferably a battery, is inserted into the casing at the other end from the send receptacle and electrically connected to the receptacle. The send unit can be used when the cable to be tested does not have a phantom power source by plugging the send receptacle into the plug end of the cable. Once the send unit is plugged therein, the battery provides a DC voltage source for the cable and energizes the cable. When the receive unit discussed above is attached to the receptacle end of the cable, the receive unit also becomes energized, thereby illuminating the LED""s according to the condition of the cable.